Markings on carton generally include contents, weight, specification, name of manufacturer, date of manufacture, price, lot number, catron number, name and address of consignee, and other data subject to change from case to case. Though data may be printed on carton in advance, it is not flexible for a production line which makes a variety of products, and results in large inventory of packaging materials. For marking of data subject to change from case to case, robber chop, spray printing with paper pattern, label or hand writing are applied and all such methods are of inefficient, and not matching with the integrated process in modern packing works.
Printing by sprayer is a feasible resolution for marking on carton. That is, within the principle of forming a marking by dot matrix, using if a vertical row of fixed nozzles to spray ink to the surface of a moving carton to print the markings is feasible. To implement such an idea, some technical problems must be overcome: 1. Structure of nozzle set must be capable of satisfy number of nozzles required for different size of marking, expansion of nozzle set must be easy, and precise nozzle must have effective measures to prevent from contamination and blockade; 2. Solenoid valve of quick response (such as operating at a frequence of up to 300 Hz) and adjustable; 3. Ink supply device must be incorporated with level indicator and have measures which allow replenishment of ink without interruption of ink supply to the nozzles; and 4. Its control device must be capable to edit, save and retrieve marking data, and control spraying of ink according to the position and moving speed of the object to be printed.
U.S. Pat. No. 4,378,564 discloses a representative prior art which comprises an ink source, control means and sprayer to form an ink jet printing apparatus. Its sprayer is an assemble of nozzles and solenoid vlaves, but direct expansion of nozzle set is not possible, and its solenoid valve is of unadjustable. Furthermore, replenishment of ink requires interruption of ink supply to nozzles, and its control means can't control ink spraying in response to the speed of the object. Therefore, the prior art is not satisfactory enough.